1. Field of the Invention
This invention relates to hydraulic drives, and particularly to a hydraulic drive that is driven by a hybrid power supply.
2. Description of the Related Art
Many work vehicles make use of hydraulic systems. For example, consider a traditional utility truck used for servicing residential telephone, electric and cable supplies. Such vehicles with hydraulic systems on-board are virtually ubiquitous in industry. The hydraulic systems provide users with a number of advantages, such as rapid deployment, convenience of use, as well as a robust power supply for tooling (such as hydraulically driven drills). However, such hydraulic systems are not without disadvantages.
Consider that many tasks facilitated by operation of hydraulic systems involve work of a prolonged duration. Accordingly, power supplies on-board the work vehicle are often inadequate to drive the hydraulic system for the duration of the work. One solution is to idle the work vehicle and make use of mechanical output from an engine of the work vehicle. Unfortunately, this is not economic in terms of fuel consumption or vehicle wear. Further, this is of increasing concern to regulatory agencies. More specifically, as the Environmental Protection Agency has pronounced that it does not have the power to enact a nationwide anti-idle law, many states, counties and municipalities have enacted their own rules regarding idling of work vehicles. Given the great variety of these rules, operators of work vehicles are challenged to rely upon traditional methods for powering hydraulic systems on-board work vehicles.
One example of an effort to address the need is provided in U.S. Pat. No. 7,104,920, entitled “Hybrid vehicle powertrain system with power take-off driven vehicle accessory” discloses a hybrid vehicle powertrain system that includes a first prime mover, a first prime mover driven power transmission mechanism having a power take-off adapted to drive a vehicle accessory, and a second prime mover. The second prime mover is operable to drive the power transmission mechanism alone or in combination with the first prime mover to provide power to the power take-off through the power transmission mechanism. The patent further discloses methods for operating a hybrid vehicle powertrain system. Unfortunately, the technology provided in this example has certain drawbacks. By way of example, having a powertrain system that includes the second prime mover, such as an electric or hydraulic motor, may cause excess wear and inefficient operation, among other things.
Accordingly, what are needed are techniques for powering hydraulic systems used in work vehicles. Preferably, the techniques minimize vehicle wear, fuel consumption and are compliant with ant-idle rules and regulations.